Electron beam generating devices may be used in sterilization of items, such as for example in sterilization of packaging material, food packages or medical equipment, or they may be used in curing of e.g. ink. Generally, these devices comprise an electron exit window assembly formed by at least a foil and a support plate. The support plate, which is preferably made of copper, has a plurality of apertures through which the electrons will be exited from the electron beam generating device during operation. The support plate forms a wall of a vacuum-tight housing of the electron beam generating device, and to sustain the vacuum the support plate apertures are covered by a foil. Said foil has a thickness of around 6-10 μm and is preferably made of titanium. Due to the thinness most of the electrons are able to pass through it.
The foil is sealed to the support plate at or near its circumference by bonding. The term bonding should here be interpreted as a general term. Possible bonding techniques may be laser welding, electron beam welding, brazing, ultrasonic welding, diffusion bonding and gluing.
During the delicate handling of the foil in the assembly process surplus foil may arise, for example due to the foil being stretched or in other ways. As the foil and the support plate are fixed to each other at the bonding line, the surplus foil may cause wrinkles in the foil upon application of vacuum in the housing. Large wrinkles are detrimental for the operation of the electron beam generating device, not only because of the reduced efficiency to let electrons pass, but also because of the risk of cracks arising along the wrinkles. The foil is indeed very fragile.